In the related art, as a tank configured to store a cryogenic liquid such as liquefied natural gas (LNG) or the like, a double shell structure tank constituted by an outer tank and an inner tank is known. In such a double shell structure tank, granular perlite serving as a cold insulation agent is filled in a space between the outer tank and the inner tank to form a cold insulation layer (see Patent Document 1). In addition, in order to prevent collapse of the inner tank due to a pressure difference between the outside (the cold insulation layer) and the inside of the inner tank, a resilient blanket (hereinafter, simply referred to as a blanket) is installed at a shell plate (an outer wall surface) of the inner tank.